Injured or damaged parts of the hard- and/or soft tissue of the human body are restored the best by using autologous hard- and/or soft tissue. This is not always possible for various reasons, which is why in many cases synthetic material is used as a temporary (biodegradable or post-operatively removable, respectively) or permanent replacement material.
Implants which are anchored in hard- and/or soft tissue, serve the temporary or permanent replacement or the support of parts of the musculoskeletal system which have been damaged by accident, use, deficiency or disease, or which have been otherwise degenerated, including especially parts of the chewing apparatus. A synthetic, chemically stable material, which is introduced into the body as a plastic replacement or for mechanical enforcement is normally called an implant (see e.g. Roche Lexikon Medizin, Urban & Fischer (Pubis.); 5th edition 2003). The support- and replacement function in the body is taken over on the basis of the mechanical features and the implant design. Hence, for instance hip- and knee joint prostheses, spine implants and dental implants have been clinically used successfully for many years.
For the anchoring of the implant and the compatibility of the implant at the interface between the implant surface/neighboring tissue, the implant surface has a great significance. Hence, measurements have shown that, almost independently of the basic material used, implants with a smooth surface are anchored only poorly in the bone (poor osteointegration), while implants with a structured surface enter into a good mechanical- and, in case of a corresponding design of the surface, also a good biological connection with the surrounding hard- or soft tissue (see e.g. Titanium in Medicine, Material Science, Surface Science, Engineering, Biological Responses and Medical Applications Series: Engineering Materials, Brunette, D. M.; Tengvall, P.; Textor, M.; Thomsen, P. (Eds.)).
The time necessary for a sufficient ingrowth, which is an important and central feature for implants, is termed osteointegration time, or, in the dental field also osseointegration time, respectively. Thereby, the time is described, which passes by until the bone substance has connected with sufficient force and durably with the implant surface, so to speak, until it has virtually integrated into the implant surface.
Various methods are used for surface treatment and surface structuring, see e.g. A Guide to Metal and Plastic Finishing (Maroney, Marion L.; 1991); Handbook of Semiconductor Electrodeposition (Applied Physics, 5) (Pandey, R. K., et al.; 1996); Surface Finishing Systems: Metal and Non-Metal Finishing Handbook-Guide (Rudzki, George J.; 1984); Titanium in Medicine, Material Science, Surface Science, Engineering, Biological Responses and Medical Applications Series: Engineering Materials, (Brunette, D. M.; Tengvall, P.; Textor, M.; Thomsen, P. (Eds.)); and Materials and Processes for Surface and Interface Engineering (NATO Asi Series. Series E, Applied Sciences, 115, Pauleau, Ives (Editor); 1995); and the references cited therein.
Implants nowadays are produced of various materials, such as for example of titanium, niobium, zirconium, tantalum, of alloys such as e.g. titanium alloys, implant steel, of CoCr alloys, of various polymers and ceramics e.g. on the basis of zirconium oxides, aluminium oxides, titanium oxides, etc.
Besides the mechanical methods of treatment, implants for example can also be produced by a combination of casting and sintering. These methods are known for metal as MIM (Metal Powder Injection Molding) and for ceramics as CIM (Ceramic Injection Molding), such as e.g. from US 2004/0038180.
For the production of dental implants, both methods can also be coupled, as is described in EP 1 570 804 A1. Furthermore, a combination with mechanical treatment of the implant produced by MIM or CIM is possible, such as for example is described in EP 1 570 804 A1, that, following sintering, the surface can be post-treated either by a blasting treatment or by chemical surface modification (e.g. acid etching).
For many implants, especially for dental implants, mainly titanium and its alloys are used, as these materials have a sufficiently low elasticity module and a relatively high stability. However, measurements have shown that titanium implants with a smooth surface structure are only insufficiently anchored in the bone, while implants with a roughened surface result in a noticeably improved bone implant connection with respect to the traction- and torsion resistance.
In EP 0 388 576 A1, it is thus suggested to apply in a first step a macro-roughness onto a metallic implant surface by sand blasting, and to subsequently overlay it with a micro-roughness by a treatment in an acid bath. Thereby, the implant surface can be roughened by sand blasting and subsequently treated with an etching agent, e.g. hydrofluoric acid or a hydrochloric acid/sulphuric acid mixture. By this structuring of the surface, a safe connection between hard tissue and metal is achieved.
In the area of dental implants, titanium, especially in the visible front oral area, is unsuitable for aesthetic reasons, as the material optically differs from the hard- and the visible soft tissue environment. It is therefore desirable to use a different material which doesn't show these disadvantages. Ceramic materials, such as zirconium oxide, titanium oxide or aluminum oxide or mixtures thereof, materials are available, which show an extremely high stability, especially, if the form bodies are compressed hot-isostatically or post-compacted hot-isostatically. A specific yttrium-stabilized zirconium oxide ceramic, which has about 92.1-93.5 weight-% ZrO2, 4.5-5.525 weight-% Y2O3 and 3.8-2.2 weight-% HfO2, is for example known from U.S. Pat. No. 6,165,925. Other prevalent ceramics are discussed in the introductory part of U.S. Pat. No. 6,165,925 extremely high stability,
The use of ceramics, for example of a zirconium oxide ceramic, a titanium oxide ceramic, or an aluminium oxide ceramic, as a material for the production of an implant anchored in the hard- or soft tissue, is tedious, as it is necessary for a sufficient mechanical stability of the ceramic to be produced without measurable porosity, normally simultaneously resulting in a smooth, extremely hard surface.
For smooth ceramic surfaces, no direct and sufficiently mechanically stable connection with the surrounding hard tissue is to be expected. Therefore, implants of pure ceramics such as zirconium oxide, titanium oxide or aluminium oxide, or mixtures thereof, have hardly been used so far in the direct contact with hard tissue. For the anchoring in hard tissue, constructive connections with metallic implant materials are used, for example in hip prosthetics or in oral implantology.
For example, in DE 195 30 981 A1, a pre-fabricated fully ceramic implant construction of zirconium dioxide is described for the dental coloured design of artificial crown stubs carried by implants. The actual implant therein consists of surface-structured metallic titanium, the aesthetics of the visible part being displayed via a zirconium oxide ceramic.
In WO 2004/096075 A1, a dental implant of a one-piece base body is described, consisting of zirconium oxide or of a zirconium oxide/aluminium mixture. A surface treatment is not described, and it is questionable whether such an implant structure shows a sufficient osseointegration at all.
FR 2 721 196 A1 describes a one-piece implant based on zirconium oxide. For the improvement of the osteointegration, the corresponding implant part shall be provided with a coating, for example of hydroxyapatite.
In WO 03/045268 A1, a ceramic implant on the basis of zirconium oxide is described. The external surface of the anchoring part is at least partially either roughened by an erosive method, or micro-structured, or provided with a coating. Therein, after a blasting treatment, such as by sand-blasting, also chemical methods, especially etching methods are taken into consideration, which can be applied partially supplementary as a post-treatment to a previous mechanical treatment. Especially preferred is first a blasting treatment, such as by sand-blasting with Al2O3, and subsequently an etching treatment, with phosphoric acid, sulphuric acid, hydrochloric acid, or mixtures thereof. Furthermore, the treated implant can be stored in a suitable fluid, for example de-ionized water, or in a NaCl-solution. Thereby it is avoided that the surface loses its activation completely or partially by components of the air prior to the insertion of the dental implant. This is how an osteointegration is supported.
The problem therein is, that with such a combined treatment, the depth of the roughness remains small due to the high hardness of the zirconium oxide ceramic, and that the ceramic is chemically extremely stable with respect to the treatment with phosphoric acid, sulphuric acid, hydrochloric acid, or mixtures thereof.
In DE 10 2005 013 200, a two-part ceramic implant is described, including a micro- and macro-structuring and the chemical or biochemical/pharmaceutical modification, respectively, of the surfaces or selected surfaces of the implant, respectively. A method for achieving this surface structure or the surface modification is not specifically described.